You might think a Brutalist-style concrete structure would be out of place in a lush, beach-resort island like Vieques. However, to preserve the natural enclave off the coast of Puerto Rico, architect John Hix went as green as possible for his hotel Casa Solaris.

Passive heating and cooling are both cost-efficient measures that ease a new residence's burden on the earth. From super-green homes to certified Passive Houses, here are six great examples of the genre.